Systems and methods for a cooled nitric oxide generator

ABSTRACT

Systems and methods for a nitric oxide (NO) generation system are provided. In particular, the present disclosure provide an NO generation system that is configured to be cooled to maintain an NO generator of the system at or below temperatures safe for patient use and contact. In some non-limiting examples, the NO generation system may include a pump configured to furnish a fluid (e.g., a gas) toward and/or through the NO generator to provide cooling thereto.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is based on and claims priority to U.S.Provisional Patent Application No. 62/480,320, filed on Mar. 31, 2017and U.S. Provisional Patent Application No. 62/558,882, filed on Sep.15, 2017. Each of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

BACKGROUND

The present disclosure relates generally to electric plasma synthesis ofnitric oxide (NO) from gases and, more specifically, to systems andmethods for a cooled NO generator to be used in medical applications.

NO is a crucial mediator of many biological systems, and is known toselectively regulate pulmonary arterial and systemic pressure, help theimmune system kill invading parasites that enter cells, inhibit thedivision of cancer cells, transmit signals between brain cells, andcontribute to the death of brain cells that debilitates people withstrokes or heart attacks, among other things. NO mediates the relaxationof smooth muscle present, for example, in the walls of blood vessels,bronchi, the gastrointestinal tract, and urogenital tract.Administration of NO gas to the lung by inhalation has been shown toproduce localized smooth muscle relaxation within the lung's bloodvessels and is widely used to treat pulmonary hypertension, pneumonia,hypoxemic respiratory failure of a term newborn, etc. without producingsystemic side effects such as systemic vasodilation and hypotension.

Inhaling NO can immediately produce potent and selective pulmonaryvasodilation that improves the matching of ventilation with perfusion,thereby increasing an injured lung's oxygen transport efficiency, andbreathing NO can raise the arterial oxygen tension. Breathing NOproduces the rapid onset of pulmonary vasodilator action occurringwithin seconds of commencing breathing with the absence of systemicvasodilatation. Once inhaled, NO diffuses through the pulmonaryvasculature into the bloodstream, where it is rapidly inactivated bycombination with oxyhemoglobin (the NO dioxygenation reaction).Therefore, the vasodilatory effects of inhaled NO are limited to thelung in the treatment of acute and chronic pulmonary hypertension.Inhaled NO can also be used to prevent ischemia reperfusion injury afterpercutaneous coronary intervention in adults with heart attacks.Furthermore, inhaled NO can produce systemic anti-inflammatory andanti-platelet effects by increasing the levels of circulating NObiometabolites (including cyclic guanosine monophosphate) and by othermechanisms, such as the oxidation of circulating ferrous hemoglobin toferric hemoglobin (methemoglobin) in the plasma. Further still, NO hasknown anti-microbial activity.

BRIEF SUMMARY

In one aspect, the present disclosure provides a nitric oxide generationsystem that includes a nitric oxide generator. The nitric oxidegenerator includes a housing having a first end and a generally opensecond end, a pair of electrodes enclosed within the housing, and areaction chamber defined between the pair of electrodes and the housing.The nitric oxide generation system further includes a scavenger housinghaving a scavenger and a filter arranged therein. The scavenger housingis configured to be removably attached to the second end of the housing.The nitric oxide generation system further includes a power supplyconnected to the pair of electrodes, and a controller in communicationwith the pump and the power supply. The controller is configured toselectively instruct the power supply to provide power to the pair ofelectrodes to generate one or more electric discharges therebetween togenerate nitric oxide within the reaction chamber. The nitric oxidegeneration system further includes a pump configured to provide fluidflow and a flow tube configured to provide fluid communication betweenthe pump and the reaction chamber. The fluid flow provided from the pumpto the reaction chamber is configured to cool the nitric oxide generatorand aid in the diffusion of the generated nitric oxide from the reactionchamber.

In one aspect, the present disclosure provides an apparatus forgenerating nitric oxide that includes a housing having a first end, agenerally open second end, and a cavity arranged between the first endand the second end, a pair of electrodes arranged within the cavity ofthe housing, and a reaction chamber defined between the pair ofelectrodes and the housing. The pair of electrodes are configured togenerate one or more electric discharges therebetween to generate nitricoxide within the reaction chamber. The apparatus further includes ascavenger housing having a scavenger and a filter arranged therein. Thescavenger housing is configured to be removably attached to the secondend of the housing. The apparatus further includes a flow tube extendingthrough the housing and into the reaction chamber to provide fluidcommunication between a pump and the reaction chamber. The fluid flowprovided from the pump to the reaction chamber is configured to cool tothe nitric oxide generator and aid in the diffusion of the generatednitric oxide from the reaction chamber.

In one aspect, the present disclosure provides a method of cooling anitric oxide generator configured to electrically generate nitric oxidegas via electric plasma discharge between a pair of electrodes. Thenitric oxide generator includes a housing enclosing the pair ofelectrodes and defining a reaction chamber between the pair ofelectrodes and the housing. The method includes providing a pumpconfigured to provide fluid flow, connecting a flow tube between thepump and the reaction chamber to provide fluid communicationtherebetween, and flowing fluid from the pump to the reaction chamberalong the flow tube, thereby cooling the nitric oxide generator.

The foregoing and other aspects and advantages of the disclosure willappear from the following description. In the description, reference ismade to the accompanying drawings, which form a part hereof, and inwhich there is shown by way of illustration a preferred configuration ofthe disclosure. Such configuration does not necessarily represent thefull scope of the disclosure, however, and reference is made thereforeto the claims and herein for interpreting the scope of the disclosure.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be better understood and features, aspects andadvantages other than those set forth above will become apparent whenconsideration is given to the following detailed description thereof.Such detailed description makes reference to the following drawings.

FIG. 1 is a schematic illustration of a nitric oxide generation systemaccording to one aspect of the present disclosure.

FIG. 2 is a detailed schematic of a nitric oxide generator within thenitric oxide generation system of FIG. 1 according to one aspect of thepresent disclosure.

FIG. 3 is a detailed schematic of the nitric oxide generator of FIG. 2with a tube entering radially into the generator according to one aspectof the present disclosure.

FIG. 4 is a detailed schematic of the nitric oxide generator of FIG. 2with a tube entering at an angle into the generator according to oneaspect of the present disclosure.

FIG. 5 is a flowchart outlining steps for operating the nitric oxidegeneration system of FIG. 1.

FIG. 6 is an illustration of a setup used to test the nitric oxidegeneration system of FIG. 1.

FIG. 7 is a schematic illustration of the test setup of FIG. 5.

FIG. 8A is an illustration of a prototype of the nitric oxide generatorof FIG. 2 with a 0.8 gram scavenger removably attached to a housingaccording to one aspect of the present disclosure.

FIG. 8B is an illustration of a prototype of the nitric oxide generatorof FIG. 2 with a 1.6 gram scavenger removably attached to a housingaccording to one aspect of the present disclosure.

FIG. 9 is a graph illustrating a voltage and current waveforms as afunction of time that were supplied to electrodes during testing of theprototypes of FIGS. 8A and 8B.

FIG. 10 is a graph illustrating nitrogen dioxide (NO₂) concentrationgenerated by the prototype generator of FIG. 8A as a function of timeduring a three day test while generating 40 ppm of nitric oxide (NO).

FIG. 11 is a graph illustrating a temperature of the prototype generatorof FIG. 8A as a function of time during a three day test whilegenerating 40 ppm of nitric oxide (NO).

FIG. 12A is a graph illustrating ozone (O₃) concentration generated bythe prototype generator of FIG. 8A with and without the 0.8 gramscavenger as a function of generated nitric oxide (NO) concentration.

FIG. 12B is a graph illustrating ozone (O₃) concentration generated bythe prototype generator of FIG. 8A with and without the 0.8 gramscavenger as a function of oxygen (O₂) concentration input to theprototype device.

FIG. 12 C is a graph illustrating ozone (O₃) concentration generated bythe prototype generator of FIG. 8A with the 0.8 gram scavenger forvarious inspired oxygen concentrations (FiO₂).

FIG. 13 is a table illustrating a concentration of nickel, iridium, andplatinum output by the prototype generator of FIG. 8A using variousscavenger and filter combinations during a twenty-four hour testgenerating 40 ppm nitric oxide (NO).

FIG. 14 is a graph illustrating a right ventricular systolic pressure(RVSP) as a function of time in anesthetized rabbits with acutepulmonary hypertension, due to U46619 infusion, inhaling variousconcentrations of nitric oxide (NO) generated by the prototype generatorof FIG. 8A and inhaling 40 ppm nitric oxide (NO) from a NO/N₂ tank.

FIG. 15 is a graph illustrating a right ventricular systolic pressure(RVSP) as a function of time in anesthetized rabbits with acutepulmonary hypertension, due to U46619 infusion, inhaling 80 ppm ofnitric oxide (NO) generated by the prototype generator of FIG. 8Atriggered on every breath, every other breath, and every third breath.

DETAILED DESCRIPTION

The use of the term “fluid” herein relates to a phase of matter and mayrelate to a liquid, a gas, or a two-phase liquid and gas.

The use of the terms “downstream” and “upstream” herein are terms thatindicate direction relative to the flow of a fluid. The term“downstream” corresponds to the direction of fluid flow, while the term“upstream” refers to the direction opposite or against the direction offluid flow.

As will be described, the present disclosure provides a nitric oxide(NO) generation system that is a fully portable, lightweight, and canreliably and safely generate NO at concentrations useful in medicalapplications and at the point-of-care. Generally, some non-limitingexamples of the present disclosure provide an NO generation system thatis configured to be cooled to maintain an NO generator of the system ator below temperatures safe for patient use and contact. In somenon-limiting examples, the NO generation system may include a pumpconfigured to furnish a fluid (e.g., a gas) toward and/or through the NOgenerator to provide cooling thereto. The fluid flow provided by thepump may also increase the efficiency of NO generation, facilitate thediffusion of freshly generated NO, and aid in preventing at least aportion of exhaled carbon dioxide (CO₂) from entering the system.

FIG. 1 illustrates one non-limiting example of an NO generation system100 according to the present disclosure. The NO generation systemincludes a controller 102, a power supply 104, a pump 106, an NOgenerator 108, and a filter/scavenger 110. In some non-limitingexamples, the power supply 104 may be a resonant power supply. Thecontroller 102 is in communication with the power supply 104 and thepump 106. In some non-limiting examples, the controller 102 may beconfigured to selectively instruct the power supply 104 to provide powerto the NO generator 108, which results in the generation of a desiredconcentration of NO gas to be supplied to a patient. For example, thecontroller 102 may be configured to selectively trigger the power supply104 based on one or more inputs, such as, an inspiration event. Theinspiration event may be detected via one or more characteristics of thepatient's respiration. For example, fluid flow rate, temperature,pressure, oxygen (O₂) concentration, CO₂ concentration, thoracic volume,etc. Alternatively or additionally, the controller 102 may be configuredto receive one or more inputs from a ventilator to determine when totrigger the NO generator 108 during or before an inspiration event.

In some non-limiting examples, the controller 102 may be configured toinstruct the NO generator 108 to produce a desired concentration of NOfor a predetermined about of time during or before each inspirationevent. In some non-limiting examples, the controller 102 may beconfigured to instruct the NO generator 108 to produce a desiredconcentration of NO for a predetermined amount of time during or beforeevery other inspiration event. In some non-limiting examples, thecontroller 102 may be configured to instruct the NO generator 108 toproduce a desired concentration of NO for a predetermined amount of timeduring or before every third inspiration event, or at larger gapsbetween inspiration events (e.g., every fourth, fifth, or sixthinspiration event, etc.).

In some non-limiting examples, the power supply 104 may be configured toprovide power to the pump 106. In these non-limiting examples, thecontroller 102 may be configured to selectively instruct the powersupply 104 to provide power to the pump 106 to facilitate fluid flowinto and/or through the NO generator 108. In some non-limiting examples,the pump 106 may be integrated with a native power supply or may bepowered via another external power supply separate from the power supply104. In these non-limiting examples, the controller 102 may beconfigured to selectively instruct the pump 106 to furnish fluid flow(from low to high ml/min or vice versa) into and/or through the NOgenerator 108.

The controller 102 may be configured to control a fluid flow rateprovided by the pump 106 to the NO generator 108. In some non-limitingexamples, the controller 102 may be configured to maintain a temperatureof the NO generator 108 within a desired temperature range bycontrolling the fluid flow rate provided by the pump 106. For example,the controller 102 may be in communication with a temperature sensor 112that is configured to measure a temperature of the NO generator 108 andmay be configured to control the fluid flow rate provided by the pump106 based on the temperature measured by the temperature sensor 112.Alternatively or additionally, the temperature sensor 112 may beconfigured to measure a temperature of the fluid flow exiting thefilter/scavenger 110 being provided to the patient, and the controller102 may be configured to control the fluid flow rate provided by thepump 106 to maintain the exiting fluid flow to the patient within adesired temperature range.

The NO generator 108 is configured to generate a desired concentrationof NO gas, upon being supplied with power from the power supply 104,from ambient gases within the NO generator 108 and/or gas supplied bythe pump 106. For example, the NO generator 108 may include one or morepairs of electrodes that are configured to generate a plasma viaelectric discharge therebetween. NO gas may be synthesized from the O₂and nitrogen (N₂) in the ambient or higher pressure gases within theplasma generated via the electrode discharge. In some non-limitingexamples, a waveform (e.g., square wave, etc.) provided to the NOgenerator 108 by the power supply 104 may control a concentration of NOgenerated thereby. In some non-limiting examples, the NO concentrationgenerated by the NO generator 108 may be measured and the controller 102may control the power supply 104 to maintain the NO concentration within a desired range.

In general, the filter/scavenger 110 may include at least one filterconfigured to prevent/filter particles prior to the NO-laden gasentering the airway of a patient and a scavenger configured to control,or limit, a concentration of undesirable byproducts (e.g., NO₂ and O₃)produced by the NO generator 108. In some non-limiting examples, thefilter/scavenger 110 may be integrated into a unitary component that maybe removably attached to the NO generator 108. For example, thefilter/scavenger 110 may be a replaceable component that is configuredto be installed on the NO generator 108 and removed once the scavengerhas been exhausted. In some non-limiting examples, the filter/scavenger110 may be removably attached to the NO generator 108 via, screws, aquick-disconnect (snap on/off), a keyed feature, a removable adhesive,and/or threads.

The NO generation system 100 may be integrated into a lightweight andportable device that provides point-of-care treatment, for example, tohypoxic babies. In some non-limiting examples, the NO generator 108 maybe installed in or near an endotracheal tube that in installed in theairway of a patient. In some non-limiting examples, the NO generator 108may be installed directly in the airway of a patient as close aspossible to a mouth piece, in the inspiratory limb. However, the system100 may be used with any of a variety of subjects, which may include ahuman, other mammal, or other animal, or may be used in otherapplications that do not include a subject.

Turning to FIG. 2, in one non-limiting example, the NO generator 108includes a pair of electrodes 202 arranged within a housing 204. Theelectrodes 202 can be fabricated from or plated with tungsten carbide,carbon, iridium, titanium, platinum, rhenium, or an alloy of theaforementioned materials, or other noble inert metals. In onenon-limiting example, the electrodes 202 are fabricated from or platedwith iridium due to a lower ratio of NO₂ to NO generated by iridium whencompared to other metals, as described in International PatentApplication No. PCT/US2015/056443 ('443 International Application),which is hereby incorporated herein by reference. In other non-limitingexamples, the NO generator 108 may include two or more pairs ofelectrodes 202. The electrodes 202 are configured to create a plasmatherebetween upon electric discharge. The plasma generated by theelectrodes 202 generates NO gas, as long as nitrogen and oxygen arepresent in the atmosphere in which the NO generator 108 is placed.

The housing 204 includes a first end 206 and a second end 208longitudinally opposing one another. In some non-limiting examples, thehousing 204 may be fabricated from a metal material (e.g., aluminum).The first end 206 includes an aperture 210 that provides access to acavity 211 formed by an interior of the housing 204. The aperture 210may be dimensioned to receive an electrode insulator 212. A pair of highvoltage wires 213 extend through the electrode insulator 212 and connectthe electrodes 202 to the power supply 104. The high voltage wires 213may include wire insulation 215 except when located within the electrodeinsulator 212 (e.g. a ceramic material), which acts to electricallyinsulate and prevent shorting. In some non-limiting examples, the wireinsulation 215 may be a molded component that includes apertures for thewires 213 and a flow tube 224 to extend therethrough. In thesenon-limiting examples, the wire insulation 215 may be fabricated from anelectrical insulator and may be configured to be attached to the firstend 206 of the housing 204.

In some non-limiting examples, the second end 208 may define a generallyopen end that is configured to removably attach to a scavenger housing214. In these non-limiting examples, the scavenger housing 214 mayinclude a first filter 216, a second filter 218, and a scavenger 220arranged between the first filter 216 and the second filter 218. Whenassembled, as illustrated in FIG. 2, the first filter 216 may be inengagement with the second end 208 of the housing 204. In somenon-limiting examples, the scavenger housing 214 may be removablyattached to the housing 204 via, screws, a quick-disconnect, a keyedfeature, a removable adhesive, and/or threads.

In some non-limiting examples, the first filter 216 may be integratedinto the housing 204 and attached to the second end 208 thereof. Inthese non-limiting examples, the scavenger housing 214 may include thesecond filter 218 and the scavenger 220.

The first and second filters 216 and 218 may be configured to filterparticles prior to the gas within the housing 204 entering the airway ofthe patient. For example, the first and second filters 216 and 218 mayprevent fragments from the scavenger 220 and/or particles/vapors thatboil off from the electrodes 202 due to the high temperatures generatedduring discharge from entering the airway of a patient. In theillustrated non-limiting example, the NO generator 108 includes onefilter arranged upstream of the scavenger 220 and another filterarranged downstream of the scavenger 220. In some non-limiting examples,the first and second filters 216 and 218 may be configured to filterparticles with a diameter larger than approximately 0.22 micrometers(μm). In one configuration, the first and second filters 216 and 218 maybe a high efficiency particulate absorption (HEPA) filters. As describedin the '443 International Application, a 0.22 μm particle filterarranged upstream of a patient is sufficient to remove electrodefragments that erode and vaporize during operation. It should be knownthat the particle size filtered by the first and second filters 216 and218 is not meant to be limiting in any way, and alternative particlefilters that filter different particle sizes are within the scope of thepresent disclosure. However, the particle size filtered by the first andsecond filters 216 and 218 should be sufficiently small to maintain thesafety and health of a patient.

When the scavenger housing 214 is attached to the housing 204, thescavenger 220 is configured to be arranged downstream of the electrodes202. In operation, the scavenger 220 may be configured to controlundesirable byproducts (e.g., NO₂ and O₃) produced by the system 100. Inone non-limiting example, the scavenger 220 may be fabricated fromcalcium hydroxide (Ca(OH)₂). In another non-limiting example, thescavenger 220 may be a reductant scavenger composed of any reductant(e.g., ascorbic acid). In some non-limiting examples, NO generationsystem 100 may be configured to efficiently generate NO gas forinhalation by a patient by triggering on inspiration of the patient,which may reduce the power requirements of the system 100 and facilitatethe use of a small scavenger 220. For example, the scavenger 220 may beless than approximately 2 grams (g). In some non-limiting examples, thescavenger 220 may be between approximately 1 g and approximately 2 g. Insome non-limiting examples, the scavenger 220 may be approximately 1.6g. In some non-limiting examples, the scavenger 220 may be less thanapproximately 1 g. In some non-limiting examples, the scavenger 220 maybe between approximately 0.1 g and approximately 1 g. In somenon-limiting examples, the scavenger 220 may be approximately 0.8 g.

When assembled, a flow path may be defined through the NO generator 108that facilitates the delivery of generated NO-laden gas to a patient.The flow path may extend from a reaction chamber 222 downstream throughthe first filter 216, the scavenger 220, and to the second filter 218.In some non-limiting examples, the second filter 218 may be an outlet ofthe flow path. In some non-limiting examples, the scavenger housing 214may include a perforated outlet wall that is configured to secure thesecond filter 218 therein but allow fluid to flow therethrough.

The reaction chamber 222 may be defined as a portion of the cavity 211in the radial clearance between the electrode insulator 212 and theinner surface of the housing 204. Ambient gases within the reactionchamber 222 may undergo a chemical reaction following an electric plasmadischarge between the electrodes 202 and, in the presence of nitrogenand oxygen, NO gas may be generated to be supplied to a patient at agiven concentration. As described herein, the NO generation system 100may be triggered to only generate NO gas upon or before selectiveinspiration events of a patient to reduce power consumption and size ofthe scavenger 220. However, the electric plasma discharge between theelectrodes 202 does generate heat, which may result in heating of the NOgenerator 108 during operation. To reduce the heating effect and controla temperature of the NO generator 108, a flow tube 224 is arranged toprovide fluid communication between the reaction chamber 222 and thepump 106. In the illustrated non-limiting example, the flow tube 224extends generally axially into the first end 206 of the housing 204 at aradial location between the electrode insulator 212 and the innersurface of the housing 204.

It should be appreciated that the orientation of the flow tube 224 withrespect to the housing 204 and reaction chamber 222 may be configured toprovide a desired flow pattern and/or swirl characteristics within thereaction chamber 222. For example, as illustrated in FIGS. 3 and 4, theflow tube 224 may extend radially through the housing 204 and into thereaction chamber 222 (FIG. 3), or the flow tube 224 may extend throughthe housing 204 and into the reaction chamber 222 at an angle (FIG. 4).In some non-limiting examples, an angle defined between the flow tube224 and the outer surface of the housing 204 may be betweenapproximately zero degrees and ninety degrees.

In some non-limiting examples, the pump 106 may be configured to furnishambient air from the surrounding under increased pressure to the NOgenerator 108 via the flow tube 224. The air flow provided by the pump106 into the reaction chamber 222 may act to convectively cool the NOgenerator 108 to maintain the NO generator 108 at or below temperaturessafe for patient use and contact. In addition, the air flow provided bythe pump 106 may act to provide fresh air into the reaction chamber tofacilitate the generation of NO gas from the nitrogen and oxygen inambient air. Further, the air flow provided by the pump 106 mayfacilitate the diffusion of freshly generated NO gas to the outlet ofthe NO generator 108 and thereby to the patient. Further still, the airflow provided by the pump 108 may aid in preventing a least a portion ofexhaled CO₂ from reaching the scavenger 220. Generally, humans mayrelease approximately 50,000 ppm of CO₂ during exhalation, and CO₂ mayact to degrade the useful lifetime of the scavenger 220. Thus, it may bedesirable to inhibit or prevent exhaled CO₂ from entering the NOgenerator 108. The NO generation system 100 is configured to limit thedegradation of the scavenger 220 via exhaled CO₂ by triggeringgeneration at or before inspiration, rather than continuously during thebreathing cycle, and by supplying additional air flow into the reactionchamber 222 with the pump 108 and flow tube 224. The additional air flowprovided by the pump 106 may act to generate a slightly positivepressure inside the reaction chamber 222, when compared to ambient, andinhibit flow back into the NO generator 108 thereby preventing at leasta portion of exhaled CO₂ from reaching the scavenger 220.

As described herein, the NO generation system 100 may be used togenerate reliable and safe NO gas at the point-of-care, for example, forbabies with hypoxia. One non-limiting example of the operation of the NOgeneration system 100 will be described with reference to FIGS. 1-5.Initially, as illustrated in FIG. 5, the NO generator 108 may be coupledto an airway of a patient at step 300. For example, the NO generator 108may be assembled with the scavenger housing 214 attached to the housing204 and the outlet of the NO generator 108 may be placed in fluidcommunication with an airway of a patient. In some non-limitingexamples, the outlet of the NO generator 108 may be coupled to aventilator. In some non-limiting examples, the outlet of the NOgenerator 108 may be coupled to a breathing tube placed in the airway ofa patient.

Once the NO generator 108 is coupled to the airway of a patient at step300, generation characteristics of the NO generator 108 may bedetermined at step 302. For example, a desired concentration of NO to begenerated, an amount of time for NO to be generated after inspiration, atidal volume, a body weight, a respiratory rate, ambient temperature,and ambient pressure, among other parameters, may be input and/ordetermined by the controller 102. Based on the operating parameters, forexample, the controller 102 may determine the NO generationcharacteristics necessary to produce a desired amount of NO gas for adesired amount of time. In some non-limiting examples, the controller102 may determine the necessary number of electrode discharge groups persecond, the number of electrode discharges per group, a time (e.g., inmicroseconds) between adjacent electrode discharges within a group, anda pulse time (e.g., in microseconds) of each individual electrodedischarge supplied to the electrodes 202 by the power supply 104. Thecharacteristics determined by the controller 102 may be adjusted duringoperation, for example, to accommodate for output NO concentration,output NO₂ concentration, output O₃ concentration, ambient temperature,ambient pressure, NO generator 108 temperature, and/or measuredbiological parameters of the patient (e.g., ventricular systolicpressure, pulmonary artery pressure, etc.).

With the NO generation characteristics determined at step 302, it may bedetermined if an inspiration event of the patient is detected at step304. In some non-limiting examples, the inspiration event may bedetected by monitoring one or more breathing characteristics of apatient, such as, a fluid flow rate, temperature, pressure, oxygen (O₂)concentration, CO₂ concentration, thoracic volume, and/or ventilatoroperating parameters. If an inspiration event is detected at step 304,the NO generator 108 may be triggered to generate the desiredconcentration of NO gas for the desired amount of time after thedetected inspiration event at step 306.

One or more output parameters of the NO generation system 100 may bemonitored at step 308 and it may be determined at step 310 if the NOgeneration characteristics need to be changed based on the measuredoutput parameters. For example, output NO concentration, output NO₂concentration, output O₃ concentration, NO generator 108 temperature,and/or measured biological parameters of the patient (e.g., ventricularsystolic pressure, pulmonary artery pressure, etc.) may be monitored byand/or input to the controller 102. In some non-limiting examples, thecontroller 102 may monitor one or more of the output parameters at step308 and determine if one of the output parameters drifts outside apredetermined operating range and a change is needed at step 310. Forexample, the controller 102 may be configured to detect that thegenerated concentration of NO gas is not within a predetermined range ofthe desired concentration and, in response, alter one or more of thegeneration characteristics determined at step 302. Alternatively oradditionally, the output concentration of NO₂ and/or O₃ may be monitoredto determine if the scavenger 220 needs to be replaced. For example, apredetermined maximum concentration of NO₂ and/or O₃ for patient safetymay be established and, once this predetermined maximum concentration isapproached, it may be determined that the scavenger 220 is required tobe replaced. Due to the removable attachment between the scavengerhousing 214 and the housing 204, the scavenger 220 may be easilyreplaced by removing the current scavenger housing 214 and installing anew scavenger housing 214 with a new scavenger 220 arranged therein.

In some non-limiting examples, the temperature of the NO generator 108may be monitored and it can be determined at step 310 if the pump 106 issupplying a sufficient flow of air thereto. For example, if thetemperature of the NO generator 108 approaches a predetermined maximumvalue, the controller 102 may instruct the pump 106 to increase a flowrate of air supplied to the reaction chamber 222 to maintain the NOgenerator 108 at or below temperatures safe for patient use and contact.Alternatively or additionally, it may be determined at step 310 if NOgas has been generated for the desired amount of time. If so, the NOgenerator 108 may stop the generation of NO gas at step 312 and wait forthe next, or another, inspiration event. In some non-limiting examples,the NO generation system 100 may be configured to instruct the NOgenerator 108 to stop generation of NO gas prior to the end of, orduring, the inspiration of a patient.

The above-described steps 302-312 may be repeated for each inspirationevent to continually supply reliable and safe NO-laden gas to a patientand maintain the NO generator 108 at a temperature that is safe forpatient use and contact. Generally, the present disclosure provides a NOgeneration system 100 that utilizes a small fluid (e.g., gas) flow tocool down the NO generator 108 and, specifically the reaction chamber222. Since the small fluid flow also facilitates the diffusion ofgenerated NO, the need for high energy to produce desired levels of NOis negated. Thus, the present NO generation system 100 provides reducedenergy consumption and also limits a temperature increase in the NOgenerator 108, without the need for high energy.

Examples

The following examples set forth, in detail, ways in which the NOgeneration system 100 and/or the NO generator 108 may be used orimplemented, and will enable one of skill in the art to more readilyunderstand the principles thereof. The following examples are presentedby way of illustration and are not meant to be limiting in any way.

Test Setup and Prototype NO Generators

FIGS. 6 and 7 illustrate a test setup used to test prototype NOgenerators (FIGS. 8A and 8B). As illustrated in FIGS. 6 and 7, aprototype NO generator 400 (e.g., a prototype of the NO generator 108described herein) was placed in fluid communication with a test lung 402arranged downstream of the prototype NO generator 400. A gas analyzer403 was placed in between the prototype NO generator 400 and the testlung 402 to measure a concentration of NO (Sievers 280i Nitric OxideAnalyzer, GE Analytical Instruments, Boulder, Colo.), NO₂ (CAPS NO₂monitor, Aerodyne Research Inc., Billerica, Mass.), and O₃ (EC 9810Ozone Analyzer, American Ecotech, Warren, R.I.) being supplied to thetest lung. Upstream of the prototype NO generator 400, an oxygenanalyzer 404 (MiniOX I, Ohio Medical Corporation, Gurnee, Ill.) measuredan input concentration of O₂, a pediatric ventilator 406 (Inspira asv,Harvard Apparatus, Holliston, Mass.) provided respiration to the testlung 402, and a flowmeter 408 (NICO2, Respironics) measured the fluidflow rate input to the prototype NO generator 400.

The prototype generators illustrated in FIGS. 8A and 8B were constructedwith the wire insulator 215 attached to the first end 206 of the housing204 and the scavenger housing 214 removably attached to the second end208 of the housing 204 via a plurality of fastening elements 410 (e.g.,screws or bolts). The prototype NO generator of FIG. 8A was constructedwith a 0.8 g scavenger and weighed approximately 14 g. The prototype NOgenerator of FIG. 8B was constructed with a 1.6 g scavenger and weightedapproximately 20 g. Thus, the constructed prototype NO generators arevery lightweight, which aids in the portability thereof and the abilityto provide NO-laden gas at the point-of-care.

Each of the prototype NO generators includes two iridium dischargeelectrodes, a scavenger comprising Ca(OH)₂, two 0.22 μm HEPA filtersarranged on opposing ends of the scavenger, and a flow tube extendingtherein to facilitate cooling and NO delivery. These components weresurrounded by a ceramic insulator, which was encased inside an aluminumhousing. The electrodes were powered by a microcontroller circuit, andenergy was stored and released by an autotransformer and delivered tothe spark gap (2 mm) to create a plasma. The level of NO production wascontrolled by four pulse pattern variables, including the number ofspark groups per second, the number of spark discharges per group, thetime in microseconds (μsec) between two spark discharges, and the pulsetime in μsec. During testing, the prototype NO generator was eithersparked continuously or was triggered for sparking for 0.5 seconds atthe commencement of each inspiration, as measured by the flowmeter 408.

Measurement of Voltage and Current Waveforms

During NO generation, waveforms of voltage across the spark gap andcurrent through the iridium electrodes were captured and recorded by adigital phosphor oscilloscope (Tektronix DPO 2012B, Beaverton, Oreg.)equipped with a 1000× high voltage probe (Tektronix p6015A, Beaverton,Oreg.) and a current probe (I-prober 520, Aim & Thurlby ThandarInstruments Ltd, Cambridgeshire, UK). Voltage and current waveforms weremeasured and compared for the prototype NO generator of FIG. 8A at atidal volume of 18 mL, a respiratory rate at 40 beats/minute (bpm), anairway O₂ level 50%, and an NO concentration at 40 ppm producing 40pulses/second with a spark duration of 0.5 seconds. The electrodes werecontinuously cooled with 70 ml/min air which admixed with the 50% O₂airway gas upstream of the prototype NO generator.

Typically, the voltage and current to initiate an electric arc arehigher on the first arc than the following arcs. As illustrated in FIG.9, the initial voltage was approximately 3 kV for each 0.5 secondsparking event, and then exponentially decayed as the plasma formed andelectrodes heated. Similarly, the initial current was approximately 200mA, and then decayed gradually. The energy consumption was betweenapproximately 2 and 3 Watts (W) for generating 40 ppm NO at tidal volumeof 18 mL, respiratory rate at 40 bpm with airway O₂ level of 50%. Theother components of the NO generation system, including the air pump,high-voltage overhead, and power supply, consume about 1.5 Watts energy.Thus, the NO generation system 100 described herein provides low powerconsumption, which aids in the portability thereof and the ability toprovide NO-laden gas at the point-of-care.

Scavenging Capacity of the Ca(OH)₂ Scavenger

The scavenging capacity of the 0.8 g Ca(OH)₂ scavenger on the prototypeNO generator of FIG. 8A was tested. During the test, the pediatricventilator 406 was used to generate a tidal volume of 18 mL and arespiratory rate of 40 bpm. The airway O₂ level was set to 50% and thedesired NO concentration was 40 ppm. The flowmeter sensed airway flowand triggered the prototype NO generator. The fraction of inspiredoxygen (FiO₂) was measured at 0.48 due to injecting 70 ml/min of air viathe air tube (ID=1.6 mm). NO₂ levels were measured and recorded everyhour for the first 12 hours, and once at 24, 48, and 72 hours.Temperature changes of the aluminum housing of the prototype NOgenerator were measured with an infrared thermometer (Cole-Parmer,Vernon Hills, Ill.) every hour for the first 12 hours, and once at 24,48, and 72 hours.

As illustrated in FIGS. 10 and 11, the NO₂ levels were below 1 ppm for48 hours, and the temperature was at 30.6±0.5° C. throughout the entireNO generation test. These data suggest that, with NO generationtriggered on inspiration, 0.8 g of scavenger is sufficient to lower NO₂levels for at least for 2 days, and the temperature of the spark chamberremained constant at approximately 31° C. for 3 days.

Ozone (O₃) Levels in the Effluent Gas with or without Scavenger

An electrical discharge in O₂ may produce O₃ as a potential harmfulbyproduct. The O₃ levels produced by the prototype NO generator of FIG.8A was measured at varying NO levels and O₂ levels, and the ability ofthe 0.8 g Ca(OH)₂ scavenger to remove O₃ was tested. As illustrated inFIG. 12A, at an airflow rate of 1 L/min, O₃ levels increased withincreasing NO production. However, after passaging through thescavenger, O₃ level was reduced as low as 3 ppb with NO of 80 ppm. Withvarying O₂ levels from 21% to 80%, as illustrated in FIG. 12B, O₃ levelswere at 5.5 ppb before and 1.5 ppb after scavenger. Also, as illustratedin FIG. 12C, the O₃ levels were kept below 1.5 ppb for all O₂concentrations ranging from 21% to 100% at a gas flow rate of 1 L/minand a NO concentration of 40 ppm. This data suggests that the electricalprototype NO generator produces minimal amounts of O₃ at all O₂concentrations tested, and the 0.8 g scavenger effectively removes O₃ tothe levels well below U.S. Environmental Protection Agency (EPA) O₃limits of 80 ppb exposure for 8 hours a day.

Trace Metals in Effluent Gas Downstream of Prototype NO Generator

To measure the levels of trace metals in the effluent gas downstream ofthe prototype NO generator of FIG. 8A, 5 groups were studied as follows:(1) without scavenger and HEPA filter, (2) with scavenger and 1 HEPAfilter, (3) with scavenger and 2 HEPA filters in series, (4) withscavenger only, and (5) with 1 HEPA filter only. NO was generated at 40ppm with airflow rate of 1 L/min for 24 hrs. The effluent gas wascontinuously bubbled into 15 ml of 5% nitric acid (Optima Grade, FisherScientific, Cambridge, Mass.). All samples were collected at 24 hours,and analyzed with quadrupole inductively-coupled mass spectrometry(ICP-MS) at University of Massachusetts Mass Spectrometry Center(Amherst, Mass.).

As illustrated in the table of FIG. 13, without a filter and scavenger,nickel particles at 40 ppb were produced by the plasma after 24 hours ofNO generation at an airflow rate of 1 L/min. With an inline Ca(OH)₂ (0.8g) scavenger, but without a HEPA filter, the nickel level was reduced to1.7 ppb. With a single HEPA filter only, the nickel level was at 0.3ppb. With the NO generator followed by a 0.8 g Ca(OH)₂ scavenger and oneor two HEPA filters, nickel levels were reduced below 1 ppb, which isbelow the OSHA limit level of 1.0 mg/m³ (mg/m³=1 ppb) for metallicnickel and nickel compounds in workroom air in order to protect workersduring an 8-hour shift over a 40-hour work week. The other trace metalsof iridium and platinum were below 0.03 ppb with or without scavenger orHEPA filter, and can be ignored in the electrically generated NO gas.These data suggest that during NO generation trace amount of nickelwould be released that can be effectively blocked by a scavenger and aHEPA filter.

Study of Anesthetized Rabbits with Pulmonary Hypertension

Rabbit studies were approved by the Massachusetts General HospitalInstitutional Animal Care and Use Committee (Boston, Mass.). Fivehealthy 6-month-old male and female New Zealand White rabbits weighing3.4±0.4 kg (mean±SD) (Jackson Laboratory, Bar Harbor, Me.). Rabbits wereanesthetized (iv ketamine and fentanyl), paralyzed (rocuronium), andmechanically ventilated via tracheostomy at 6 ml/kg tidal volume, withrespiratory rate 40-50 bpm, delivered airway FiO₂ 0.5, an inspiratorytime of 0.5 seconds and PEEP 1-2 cm H₂O. Right ventricular systolicpressure (RVSP) was monitored continuously using a 4-Fr catheter(Swan-Ganz, Edwards Lifesciences, Irvine, Calif.) placed via externaljugular vein. Pulmonary hypertension was induced by increasing rightventricular systolic pressure (RVSP) for 60 minutes infusing a potentpulmonary vasoconstrictor U46619 (Cayman Chemical, Ann Arbor, Mich.).Mean arterial pressure and heart rate were monitored at baseline, duringU46619 infusion, and before and after breathing NO. The prototype NOgenerator of FIG. 8A was placed at the external end of tracheostomy tube(ID=3.5 mm), and NO was generated for 0.5 seconds on inspiration andtriggered by the flowmeter 408.

In some non-limiting applications, the prototype NO generator may bedesigned for baby ventilation to treat pulmonary hypertension. NOgenerated from the prototype NO generator was compared it to thestandard of care, NO from a NO/N₂ tank, to determine if the prototype NOwould produce vasodilation in rabbits with acute pulmonary hypertension.As illustrated in FIGS. 14 and 15, anesthetized rabbits received acontinuous infusion of the thromboxane analog U46619 over 60 mins, whichincreased RVSP from 14±2 mmHg to 28-30 mmHg. NO was generated byinspiratory plasma discharge, and then injected at 70 ml/min into theendotracheal tube. Rabbits breathed 50% O₂ and 20, 40, or 80 ppm NOproduced on inspiration by the prototype NO generator for four minutes,then NO production and delivery were stopped, and RVSP was measured foran additional five minutes. With specific reference to FIG. 14,breathing electrically generated NO rapidly reduced the RVSP from 30mmHg before NO breathing to 24 mmHg at one min after breathing NO. As acontrol, rabbits breathed 40 ppm NO diluted from a tank (500 ppm NO inN₂, Airgas, Cinnaminson, N.J.) in 50% O₂. This data indicates thatelectrically generated NO is as effective in reducing RVSP as breathingNO diluted from a convention NO/N₂ cylinder.

To save energy and reduce the consumption of the scavenger, it wastested whether sparking every two- or three-breaths on inspiration wouldreduce RVSP in rabbits with pulmonary hypertension. As illustrated inFIG. 15, NO generated on every two- or three-breaths reduced RVSP from30 mmHg to 26 mmHg in rabbits (P<0.05 differ versus before NObreathing), which indicates that triggering on every two- orthree-breaths may be effective in treating pulmonary hypertension andreduce the power consumption of the NO generation system 100 andincrease the lifetime of the scavenger 220.

Within this specification embodiments have been described in a way whichenables a clear and concise specification to be written, but it isintended and will be appreciated that embodiments may be variouslycombined or separated without parting from the invention. For example,it will be appreciated that all preferred features described herein areapplicable to all aspects of the invention described herein.

Thus, while the invention has been described above in connection withparticular embodiments and examples, the invention is not necessarily solimited, and that numerous other embodiments, examples, uses,modifications and departures from the embodiments, examples and uses areintended to be encompassed by the claims attached hereto. The entiredisclosure of each patent and publication cited herein is incorporatedby reference, as if each such patent or publication were individuallyincorporated by reference herein.

We claim:
 1. A nitric oxide generation system comprising: a nitric oxidegenerator including: a housing including a first end and a generallyopen second end; a pair of electrodes enclosed within the housing; and areaction chamber defined between the pair of electrodes and the housing;a scavenger housing including a scavenger and a filter arranged therein,wherein the scavenger housing is configured to be removably attached tothe second end of the housing; a power supply connected to the pair ofelectrodes; a controller in communication with the pump and the powersupply, wherein the controller is configured to selectively instruct thepower supply to provide power to the pair of electrodes to generate oneor more electric discharges therebetween to generate nitric oxide withinthe reaction chamber; a pump configured to provide fluid flow; and aflow tube configured to provide fluid communication between the pump andthe reaction chamber, wherein fluid flow provided from the pump to thereaction chamber is configured to cool the nitric oxide generator andaid in the diffusion of the generated nitric oxide from the reactionchamber.
 2. The nitric oxide generation system of claim 1, wherein thepair of electrodes comprise at least one of tungsten carbide, carbon,iridium, titanium, rhenium, and platinum.
 3. The nitric oxide generationsystem of claim 1, wherein the pair of electrodes comprise iridium. 4.The nitric oxide generation system of claim 1, wherein the scavenger isfabricated from calcium hydroxide.
 5. The nitric oxide generation systemof claim 1, wherein the scavenger is configured to control an amount ofundesired byproducts from the one or more electric discharges betweenthe pair of electrodes.
 6. The nitric oxide generation system of claim1, wherein the power supply comprises a resonant power supply.
 7. Thenitric oxide generation system of claim 1, wherein the scavenger housingfurther comprises a second filter arranged on an opposing side of thescavenger as the filter.
 8. The nitric oxide generation system of claim7, wherein the filter and the second filter are each configured tofilter particles with a diameter greater than approximately 0.22micrometers.
 9. The nitric oxide generation system of claim 7, whereinthe filter and the second filter each comprise a HEPA filter.
 10. Thenitric oxide generation system of claim 7, wherein the filter isconfigured to filter electrode particles upstream of an airway of apatient and to prevent granular scavenger from entering the reactionchamber, and the second filter is configured to filter electrodeparticles upstream of the airway of the patient.
 11. The nitric oxidegeneration system of claim 1, wherein a second end of the housingincludes a second filter coupled thereto.
 12. The nitric oxidegeneration system of claim 11, wherein the filter and the second filterare each configured to filter particles with a diameter greater thanapproximately 0.22 micrometers.
 13. The nitric oxide generation systemof claim 11, wherein the filter and the second filter each comprise aHEPA filter.
 14. The nitric oxide generation system of claim 11, whereinthe filter is configured to filter electrode particles upstream of anairway of a patient and to prevent granular scavenger from entering thereaction chamber, and the second filter is configured to filterelectrode particles upstream of the airway of the patient.
 15. Thenitric oxide generation system of claim 1, further comprising atemperature sensor arranged to measure at least one of a temperature ofthe nitric oxide generator and a temperature of NO-laden gas output fromthe scavenger housing.
 16. The nitric oxide generation system of claim15, wherein the controller is further configured to selectively controla fluid flow rate provided by the pump in response to the temperaturemeasured by the temperature sensor.
 17. The nitric oxide generationsystem of claim 1, wherein the controller is configured to detect aninspiration event.
 18. The nitric oxide generation system of claim 17,wherein the controller is further configured to instruct the powersupply to provide power to the pair of electrodes to generate one ormore electric discharges therebetween in response to the detection ofthe inspiration event.
 19. The nitric oxide generation system of claim18, wherein the controller is further configured to instruct the powersupply to provide power to the pair of electrodes for a predeterminedamount of time.
 20. The nitric oxide generation system of claim 1,wherein the scavenger weighs less than approximately 2 grams.
 21. Thenitric oxide generation system of claim 1, wherein the scavenger weighsless than 1 gram.
 22. The nitric oxide generation system of claim 1,wherein the scavenger weighs approximately 0.8 grams.
 23. An apparatusfor generating nitric oxide comprising: a housing including a first end,a generally open second end, and a cavity arranged between the first endand the second end; a pair of electrodes arranged within the cavity ofthe housing; a reaction chamber defined between the pair of electrodesand the housing, wherein the pair of electrodes are configured togenerate one or more electric discharges therebetween to generate nitricoxide within the reaction chamber; a scavenger housing including ascavenger and a filter arranged therein, wherein the scavenger housingis configured to be removably attached to the second end of the housing;and a flow tube extending through the housing and into the reactionchamber to provide fluid communication between a pump and the reactionchamber, wherein fluid flow provided from the pump to the reactionchamber is configured to cool the nitric oxide generator and aid in thediffusion of the generated nitric oxide from the reaction chamber. 24.The apparatus of claim 23, wherein the pair of electrodes comprise atleast one of tungsten carbide, carbon, iridium, titanium, rhenium, andplatinum.
 25. The apparatus of claim 23, wherein the pair of electrodescomprise iridium.
 26. The nitric oxide generation system of claim 23,wherein the scavenger is fabricated from calcium hydroxide.
 27. Thenitric oxide generation system of claim 23, wherein the scavenger isconfigured to control an amount of undesired byproducts from the one ormore electric discharges between the pair of electrodes.
 28. The nitricoxide generation system of claim 23, wherein the power supply comprisesa resonant power supply.
 29. The nitric oxide generation system of claim23, wherein the scavenger housing further comprises a second filterarranged on an opposing side of the scavenger as the filter.
 30. Thenitric oxide generation system of claim 29, wherein the filter and thesecond filter are each configured to filter particles with a diametergreater than approximately 0.22 micrometers.
 31. The nitric oxidegeneration system of claim 29, wherein the filter and the second filtereach comprise a HEPA filter.
 32. The nitric oxide generation system ofclaim 29, wherein the filter is configured to filter electrode particlesupstream of an airway of a patient and to prevent granular scavengerfrom entering the reaction chamber, and the second filter is configuredto filter electrode particles upstream of the airway of the patient. 33.The nitric oxide generation system of claim 23, wherein a second end ofthe housing includes a second filter coupled thereto.
 34. The nitricoxide generation system of claim 33, wherein the filter and the secondfilter are each configured to filter particles with a diameter greaterthan approximately 0.22 micrometers.
 35. The nitric oxide generationsystem of claim 33, wherein the filter and the second filter eachcomprise a HEPA filter.
 36. The nitric oxide generation system of claim33, wherein the filter is configured to filter electrode particlesupstream of an airway of a patient and to prevent granular scavengerfrom entering the reaction chamber, and the second filter is configuredto filter electrode particles upstream of the airway of the patient. 37.The nitric oxide generation system of claim 23, further comprising atemperature sensor arranged to measure at least one of a temperature ofthe nitric oxide generator and a temperature of NO-laden gas output fromthe scavenger housing.
 38. The nitric oxide generation system of claim37, wherein the controller is further configured to selectively controla fluid flow rate provided by the pump in response to the temperaturemeasured by the temperature sensor.
 39. The nitric oxide generationsystem of claim 1, wherein the controller is configured to detect aninspiration event.
 40. The nitric oxide generation system of claim 39,wherein the controller is further configured to instruct the powersupply to provide power to the pair of electrodes to generate one ormore electric discharges therebetween in response to the detection ofthe inspiration event.
 41. The nitric oxide generation system of claim40, wherein the controller is further configured to instruct the powersupply to provide power to the pair of electrodes for a predeterminedamount of time.
 42. The nitric oxide generation system of claim 21,wherein the scavenger weighs less than approximately 2 grams.
 43. Thenitric oxide generation system of claim 21, wherein the scavenger weighsless than 1 gram.
 44. The nitric oxide generation system of claim 23,wherein the scavenger weighs approximately 0.8 grams.
 45. A method ofcooling a nitric oxide generator configured to electrically generatenitric oxide gas via electric plasma discharge between a pair ofelectrodes, the nitric oxide generator including a housing enclosing thepair of electrodes and defining a reaction chamber between the pair ofelectrodes and the housing, the method comprising: providing a pumpconfigured to provide fluid flow; connecting a flow tube between thepump and the reaction chamber to provide fluid communicationtherebetween; flowing fluid from the pump to the reaction chamber alongthe flow tube, thereby cooling the nitric oxide generator and aid thediffusion of newly generated NO.